In manufacturing semiconductor elements, lithographic technology has been employed in which a photoresist coating is formed on a substrate such as a silicon wafer and, after selectively irradiating this with actinic rays, is subjected to development processing to thereby form a resist pattern on the substrate.
In recent years, in order to attain much higher degree of integration in LSI, patterning technology to form patterns with a finer line width by a lithographic process has made a rapid progress. For forming a pattern with a finer line width, various proposals have been made with respect to all steps of the lithography and all materials to be used therein including photoresists, antireflective coatings, exposing methods, exposing apparatus, developing agents, developing processes and developing apparatus. For example, Japanese Patent No. 2643056 and Japanese Unexamined Patent Publication No. H7-181685 describe that an antireflective surface layer containing a fluorine-containing compound with a low refractive index is formed on a resist layer to thereby prevent detrimental influences of reflected light from the resist surface on formation of a resist pattern. To form an antireflective layer on a resist layer provides the advantage that, since degree of vibration amplitude of the thickness of a resist coating vs. sensitivity curve becomes smaller, fluctuation in sensitivity of resist becomes smaller even when thickness of the resist layer fluctuates, which leads to a decreased fluctuation in dimension of resist patterns formed. In addition, antireflective surface layer serves to decrease standing wave to be caused by interference between incident light and reflected light or between one reflected light and another reflected light. Recently, technology of forming a resist pattern having a desired line width without providing the antireflective surface layer has also been developed. For example, an underlying substrate is made plane to depress fluctuation in dimension due to fluctuation in thickness of the resist layer as described above, or a mask pattern is finely adjusted according to fluctuation in dimension of the resist.
With regard to exposing apparatus, there has been proposed a process of using a light source emitting radiation of a short wavelength, which is advantageous for forming a finer pattern, such as deep UV rays of KrF excimer laser (248 nm) or ArF excimer laser (193 nm) or, further, X rays or electron beams, and some of them have been coming into practice.
On the other hand, improvement in the yield of semiconductor integrated circuits has occupied the attention as an extremely important matter in manufacturing them. There exist many factors that decide the yield of semiconductor integrated circuits. One of the factors is patterning failure upon forming a pattern using a resist. This patterning failure of a resist pattern is caused, for example, by dust existing in or on the surface of the resist, by deterioration of the resist due to floating chemical species in a clean room, by coating failure of the resist or the like, or by development failure. As an example of deterioration due to chemical species in a clean room, there is illustrated that which is caused in the process using a chemically amplified photoresist. In this process, the chemically amplified photoresist is so susceptible to the influence of acidic substances, basic substances and moisture in the atmosphere that there results a change in dimension of a pattern—for example, a T-topped resist pattern results when a positive-working photoresist is used, or a round-topped resist pattern results when a negative-working photoresist is used—in case when the period between patternwise exposure to PEB (post exposure bake) is prolonged or due to intermixing with a resist.
In addition, defects upon developing a resist coating have become a problem. For example, there are illustrated scumming in line-and-space type resists and opening failure in contact hole type resists. Several causes may be considered for the opening failure of contact holes, but the most popular opening failure is that which is caused by residues after development. As the causes for these defects, there is illustrated insufficient dissolution of exposed portions into a developing solution due to insufficient contact between the developing solution containing water as a major component and the surface of a resist upon bringing the developing solution into contact with the resist surface, which leads to opening failure of portions which are designed to open. It is also possible that insolubles for the developing solution might re-deposit onto the surface of the resist upon rinsing with water after development.
Further, it is necessary to enhance contrast of a resist in order to form a finer pattern. In general, in order to improve contrast of a contact hole type resist, a technique of increasing a protecting ratio of hydrophilic groups in a major component polymer is used with respect to, for example, positive-working chemically amplified photoresists. However, when the protecting ratio is increased, the resist surface is liable to become hydrophobic, leading to deterioration in wetting properties for the developing solution.
Various investigations have been conducted to solve the above-described problems. For example, Japanese Unexamined Patent Publication No. H9-246166 proposes to treat the surface of a photoresist with plasma to thereby render the surface hydrophilic, thus improving wetting properties of the resist for a developing solution and decreasing development defects. This technique, however, requires introduction of an additional apparatus for the plasma treatment and involves the problem of decrease in throughput.
In addition, various attempts for decreasing the development defects by optimizing development sequence have been made as well. For example, Japanese Examined Patent Publication No. H4-51020 describes to improve wetting properties of a positive-working resist for a developing solution by adding an acetylenealcohol type surfactant to the developing solution, thereby forming a pattern having no development defects. Although some effects can be obtained by this technique, the effects are at present still insufficient in ultra-fine working using the aforesaid chemically amplified photoresists. In addition, Japanese Unexamined Patent Publication No. S61-179435 describes to optionally conduct surface coating, which is effective for improving wetting properties for a developing solution, in addition to the method of adding a surfactant to the developing solution and the method of plasma-treating the surface of a resist coating, for preventing development defects resulting from lack of wetting properties for the developing solution.
However, particularly in case when surface coating for decreasing the development defects is conducted on a chemically amplified photoresist, there results a T-topped pattern if the surface coating composition contains a compound, such as a basic compound, which deactivates an acid generated at patternwise exposure. On the other hand, in case when this surface coating gives an excess amount of acid to the photoresist layer, there results an extreme reduction in thickness of coating in unexposed portions, which might lead to formation of a round topped resist pattern which constitutes an obstacle in an etching process.
Further, problems in attaining uniform thickness of coating and uniform development to be caused with a recent increase in diameter of a substrate such as a silicon wafer are said to make it difficult to form a finer pattern. For example, a paddle developing method has so far been popularly employed for developing a resist coating on the silicon wafer. In the paddle developing method, a developing solution is dropped onto a resist coating formed on a substrate, and the substrate is spun to form a thin film of the developing solution all over the resist coating, thus development of the resist coating being conducted. However, there generates a difference in circumferential speed between the central portion and the peripheral portion of the substrate, thereby a difference in speed of the coating generating. Thus, developing conditions become different between the central portion of the wafer and the peripheral portion thereof. In this situation, particularly when a chemically amplified photoresist is used as a resist and a large-diameter substrate having a diameter of 8 inches or more is used, development defects in the peripheral portion are caused in some cases which have not conventionally been observed in treating a resist coating formed on a substrate having a diameter of 6 inches or less.
Therefore, in order to improve a yield in manufacturing semiconductor integrated circuits and so on, a process for forming a resist pattern has been desired earnestly which enables one to reduce development defects to be caused upon development including development defect to be caused in the periphery of a chemically amplified photoresist formed on a larger diameter substrate such as a silicon wafer, and which does not cause pattern failure such as T-top or round top after development, thus being adapted for forming a finer resist pattern.
In consideration of the above-described situation, an object of the present invention is to provide a process for forming a resist pattern which can reduce development defects of a chemically amplified photoresist, formed on a large diameter substrate having a diameter of 8 inches or more, to be caused upon development and which does not cause deterioration of pattern profiles such as T-top or round top inconvenient for an etching step due to detrimental influences of a processing atmosphere and intermixing between the surface coating and the resist, and a composition for reducing development defects in this process.